The present invention has to do with a flat-surfaced floor structure for a railroad boxcar.
The floor structure of a boxcar must support the weight of the contents of the boxcar and is carried on an underframe that is, in turn, supported by two wheeled trucks. Additionally, the floor structure must support the weight of loading machinery, such as a loaded forklift that travels within the boxcar, without suffering significant permanent deformation. One boxcar floor structure design criterion that is generally recognized in the industry is the ability to withstand a lift truck axle load of 60,000 pounds without suffering permanent deformation. Furthermore, these goals should be achieved with a minimum weight, in order to allow a maximum load to be placed in the boxcar without exceeding the maximum weight limit for a loaded boxcar. The floor surface should also be as close to the top of rail as possible, to allow as much vertical clearance within the boxcar as possible, as the height of the boxcar roof is limited by clearance requirements. Cost of manufacture is also of concern in a boxcar floor design, because boxcars are sold in a competitive market.
In the past, most boxcar floor structures have been formed so as to allow nails to be driven into the floor at various places to secure loads. In the industry this is termed a "nailable floor." Such floors are typically formed by placing abutting formed steel "planks" or channels, open side down, over the longitudinal stringers of the boxcar underframe so that nails can be inserted between and held by the abutting formed channels. Although this continues to be a useful configuration for the floor of a boxcar, there are some applications, such as hauling paper rolls or other goods having a relatively delicate exterior, for which a flat floor is preferred.
For a flat floor it is generally necessary to support a set of flat plates over the stringers. As the stringers are not typically arranged closely enough together to adequately support the plates, it is necessary to position closely spaced structural members transversely over the stringers. Heretofore, the members of choice for this function have been formed steel channels, installed with their webs, or side walls, vertical and their bases horizontal. The vertical webs, or side parts, of these channels are able to support a heavy load, whereas the horizontal, or base, portions can be attached to the stringers or provide reinforcement for the floor plates.
One floor structure that is currently available uses steel floor plates and formed channels that are both of material 3.797 mm (0.1495") thick. The formed channels are 52.3875 mm (2-1/16") wide and are spaced 50.8 mm (2") apart. This assembly is heavier than is desirable. Another floor structure also uses 3.416 mm (0.1345") thick steel sheet both as the top sheet and for formed "hat"-shaped support members. In this assembly the formed hat-shaped members are spaced with a pitch of 152.4 mm (6"). Unfortunately, this arrangement suffers permanent deformation when a loaded 60,000-pound fork lift axle load travels over it. A floor structure that is not prone to permanent deformation from the weight of a loaded 60,000-pound lift truck axle load, but that is not substantially heavier than existing floor structures would be highly desirable.
One element of boxcar underframe design that has traditionally presented a challenge to design engineers is the accommodation of the wheels of the boxcar. In most designs, the pattern of structural elements that is present over most of the area of the boxcar floor would contact the wheels if it was extended into the wheel wells. In a prior construction, to avoid this occurrence, the pattern of structural members is interrupted, forming a well to accommodate each wheel. A heavy gauge steel plate defining a through-hole for accommodation of a wheel is attached to the underframe above each wheel, to provide the needed structural strength. Unfortunately, these heavy gauge plates must be specially made and add weight to the boxcar.
In one prior art nailable floor, each formed channel plank that bridges the wheel well is reinforced with a steel plate that closes the downwardly facing channel. The extra strength imbued to the floor structure by this addition permits the omission of the heavy gauge steel plates necessary in previous designs.
What is needed, then, is a floor structure that can withstand the weight of loaded 60,000-pound fork lift axle load without suffering permanent deformation, yet is lighter and can be more economically constructed than previously existing floor structures.